Understanding how the genetic code is translated into functional proteins.
The flow of genetic information within a biological system is generally DNA → RNA → Protein.
Transcription is the synthesis of mRNA copied from the DNA base sequences by RNA polymerase.
The process occurs in a $5' \rightarrow 3'$ direction. RNA polymerase binds to a site on the DNA at the start of a gene, moves along the gene separating DNA into single strands, and pairs up RNA nucleotides with complementary bases on one strand of the DNA. There is no thymine in RNA, so uracil pairs with adenine. RNA polymerase forms covalent bonds between the RNA nucleotides.
The antisense strand is the template. The sense strand has the same sequence as the mRNA (with T instead of U).
Given the antisense strand 3'-TAC-CGA-TTC-5', the mRNA sequence is 5'-AUG-GCU-AAG-3'.
In eukaryotes, the immediate product of transcription is pre-mRNA. It must be modified to form mature mRNA.
Alternative splicing can produce different mature mRNAs from a single gene, increasing the proteome complexity.
Translation is the synthesis of polypeptides on ribosomes.
The amino acid sequence of polypeptides is determined by mRNA according to the genetic code. Codons of three bases on mRNA correspond to one amino acid in a polypeptide.
tRNA molecules have an anticodon that is complementary to an mRNA codon, and they carry the corresponding amino acid.
Translation depends on complementary base pairing between codons on mRNA and anticodons on tRNA.
Translation consists of initiation, elongation, translocation, and termination.
Many antibiotics (e.g., tetracycline) target prokaryotic ribosomes (70S) specifically, inhibiting bacterial translation without affecting eukaryotic ribosomes (80S).
Polypeptides often require modification to become functional proteins.
These modifications can include:
Test your knowledge of D1.2 Protein Synthesis:
Transcription occurs in a $5' \rightarrow 3'$ direction.
The promoter is a non-coding sequence of DNA that serves as the binding site for RNA polymerase and determines which strand will act as the template.
Introns are non-coding sequences that are removed during splicing, while exons are coding sequences that are joined together to form mature mRNA.
Three bases make up a single codon, which codes for one amino acid.
Alternative splicing is the process where some exons are removed along with introns. It is significant because it allows a single gene to code for multiple different proteins.